The present invention relates to valves and, more particularly, to a multi-position rotary selector valve.
Multi-port selector valves have been in use for many years in a variety of applications. Generally, as employed in oil fields where it is desired to isolate one of a plurality of incoming fluid streams for testing the volume and composition of the isolated stream, such valves comprise a valve body having circularly spaced apart inlet ports each of which receives fluid from a well head. The valve body cover plate rotatably mounts one end of a trunnion whose lower end is rotatably mounted in a bottom portion of the valve body. The trunnion member contains an elbow passage having an inlet nozzle that can be turned into registration with a selected one of the inlet ports for conducting the selected well stream to a test outlet in the lower end of the valve body in communication with the opposite end of the elbow passage. The non-isolated fluid streams entering through the other inlet ports commingle in a common cavity of the valve body to be exhausted through a production outlet, also formed in the lower portion of valve body.
In the prior art rotary valve, the inlet nozzle to the elbow passage comprises a hard plastic sliding seal ring mounted on a shoulder of a steel seal backup ring which, in turn, is seated upon a wavy steel seal-energizing spring ring backed up by an adjusting nut threadedly engaged within the nozzle mouth. The seal ring free-floats inside the nozzle mouth and is pressed tightly against a machined cylindrical surface of the valve body by the spring ring. As the nozzle is rotated from one port to another, the hard seal slides against the valve body wall. If a grain of sand or other particle happens to lodge in this tight fit, the plastic seal is scratched and begins to leak. Internal valve corrosion also erodes the plastic seal. In order to restore the seal, the backup nut must then be adjusted to compress the backup spring to further load the seal which, in turn, effects further erosion. In addition, as the seal ring is tightly slidably engaged with the valve body wall while turning from one position to another, the seal may itself rotate relative to its supporting ring and assume a position of its convex sealing surface which is not matingly complementary to the configuration of the machined cylindrical inner surface of the valve body on which it is intended to seat.
In addition, a higher pressure normally is obtained inside the nozzle than within the valve body cavity such that the hard plastic seal ring tends to be unseated by the differential pressure. In an effort to remedy the ensuing leakage, the only solution is to further compress the backup spring which, in turn, exacerbates seal erosion.
The prior art valve has been so prone to internal leakage that it has been customary to dedicate one of its inlet ports solely to sue as a test position in order to detect leakage and to gain access to the adjusting nut to further compress the backup spring. Such dedication of one of the inlet ports for use solely as a test position eliminates use of that port as a test site for another well and so increases equipment costs.
Other disadvantages of the prior art valve are due to the mechanism for moving and positioning the nozzle. As the nozzle seal is tightly pressed against the valve body in sliding from one port to another, a substantial amount of torque must be applied from a large motor. Also, a circular metal cam is attached to the nozzle rotating shaft to actuate one of a series of manually adjusted motor shut-off microswitches when the nozzle mouth is over the appropriate port. In field usage it has been found that this switch mechanism is not sufficiently positive in indexing the nozzle with respect to a selected port due to slipping micro switches, the use of multi-conductor cable which is prone to electrical failure, and normal deterioration of the mechanical couplings from the drive gear box to the electronic and valve mechanisms.